""Trust the Oak," said she; "trust the Oak, and the Elm, and the great Beech. Take care of the Birch, for though she is honest, she is too young not to be changeable. But shun the Ash and the Alder; for the Ash is an ogre,—you will know him by his thick fingers; and the Alder will smother you with her web of hair, if you let her near you at night.""

― Phantastes, Chapter III

In one of MacDonald's most renowned novels, Phantastes, the protagonist, while travelling in 'Fairy Land', is faced with animate trees. Tolkien remarked in a letter that this notion had "perhaps some remote influence" on his creation of the Ents.[4]

In 1964, Tolkien was asked to write a preface to an American edition of MacDonald's short story "The Golden Key". While accepting the commission, for the reason that he thought "well of this story of his", Tolkien never finished the preface, and wrote in a letter to the publishers that "I am not as warm an admirer of George MacDonald as C.S. Lewis was"[5] (Lewis, more explictly and warmingly than Tolkien, thought highly of MacDonald, writing that "I have never concealed the fact that I regarded George MacDonald as my master"[6]).

In "An Interview with Tolkien", Henry Resnick (Niekas Issue 18, 1967) Tolkien said:As a matter of fact, insofar as... without harping or preaching on the side of various rather old-fashioned things like humility, valor, and so on... and courage, you can carry [on] those over and I think it has rather an effect on people — young folks are ready in their attitudes to rather be changed. But I didn't intend these things, because I didn't write it for children. That's why I don't like George MacDonald very much; he's a horrible old grandmother. That's a very find woman figure, of course, really — the Queen is rather a mother.

Wayne G. Hammond and Christina Scull have argued that Tolkien, when re-reading "The Golden Key" and other of MacDonald's works for the preparation of the foreword, apparently reconsidered his former admiration on the grounds that the stories often contained a narrator's voice and too much of moral lecturing reminding of the literary style of The Hobbit (a style which Tolkien had regretted later in life). Hammond and Scull further quote from a manuscript, held at the Bodleian Library, where Tolkien writes that "a highly selective memory had retained only a few impressions of things that moved me, and re-reading G[eorge] M[acDonald] critically filled with me distaste".[7]